Figured I'd add to this thread rather than starting a new one. Here are a few things I would like to see:
1. Container loaders for larger aircraft? It'd be much more realistic than hooking up a small belt loader in front of those large doors on some of the bigger heavies.
2. So far, I've noticed that the belt loaders only go to the rear baggage compartments of the various aircraft I've tried with GSX. For aircraft like the 737, A319/320, and larger, most ground crews would field an extra loader of some sort to make turns and departures go by quicker.
3. De-ice trucks of course. Ideally, with real-world driving patterns for gate sprays that are associated to a particular truck type.
4. The pushback procedure seems to prompt me, the user, to select a direction and push right away before the towbar and tractor are hooked up. It would be really nice to have the towbar and tractor hooked up, and then a separate command to initiate the pushback. This would make the procedure seem a little more realistic.
5. Wands for the wing walker (most airlines and contractors I know of require wands for these guys). At the very least, it would be nice if the wing walker can pull such wands out during the final marshal.
6. Wing walkers for arrival (having the eyes of the marshaller is great, but most companies have extra people watching the wings as well when a plane comes into an equipment dense gate)
7. Not sure if this would be too complex, but most ground handling companies and airlines also have wing walkers (two of them) stand and walk near the wings of the aircraft to make sure the wings won't bang into anything. It'd be nice to see something similar.
8. Make the baggage inside the baggage carts appear more laying flat or stacked.
That's it for now. Some of these suggestions come from personal experience working on the ramp of a busy airport. I can offer a few more suggestions on de-icing and how people and equipment typically move around. Some of which probably isn't plausible in FSX, but thought I'd throw that depending on how GSX develops further